The present invention relates to an electric press.
Generally the electric press is provided with an electric motor as a drive source for moving the ram up and down relative to a work which is to be processed with application of pressure. In this connection, the electric press is generally provided with an area sensor for instantly stopping the drive source in case of emergency in order to prevent accidents, for example, in case the operator happens to come into a predetermined area around the electric press while the electric press is driven.
On the other hand, it is required that the operator enters the predetermined area in connection with the electric press to give teaching to the electric press accordingly in case the work to be processed is changed and/or the operation mode is changed. The electric press is, therefore, provided with a device for giving a muting signal to the area sensor to invalidate the same while the electric press ram is in a predetermined condition such as in a standby condition.
JP-A-10-277800 may be referred to as a prior art.
However the CPU (Central Processing Unit) may happen to run in uncontrolled condition. Under such circumstances, the danger is that the area sensor invalidating device may be operated when the electric press is not in the standby condition, and the area sensor is not operated. Therefore, the electric press may be provided with a plurality of CPU's for watching an watchdog signal to detect the uncontrolled running condition of the CPU. However this technique is not so reliable because the watchdog signal is made up by software and it is assumed that the programs may run in uncontrolled condition at the time of uncontrolled running of CPU.
It is, therefore, an object of the invention to solve the problems of the prior art.